The invention relates to a switch comprising at least two interacting contacts, a closing spring for moving the contacts into the closed position, an operating button which can be used to initiate a prestressing phase of the closing spring, and a locking device for locking the contacts, in closing the switch, until a predetermined moment at which the influence of the prestressed closing spring is to be released onto the contacts.
A switch of this nature is known from international patent application WO 96/17368.
This known switch has two interacting contacts, namely a fixed contact and a movable contact which is attached to a switch shaft by means of a contact arm. This switch shaft is rotated by means of a prestressed closing spring in order to move the said contacts into the closed position. To this end, the closing spring is firstly prestressed by rotating the actuating button. In this process, a catch is used, comprising the movement of a knee device beyond the dead centre. The result is a snap action in which the spring is fully prestressed before the contacts are released. The closing spring also takes care of the contact force. In switches of this nature, the aim is to design them in such a manner that the switch can be closed in an operator-independent manner, i.e. that the contact pressure and the closing speed are as far as possible independent of the person operating the switch. This characteristic is important since it is necessary to prevent the contacts in a switch being damaged, on the one hand by being closed too quickly, in which event the contacts may be burnt away as a result of bouncing, and on the other hand by being closed too slowly, in which case the contact pressure is built up too slowly, so that contacts may become welded in place.
The known switch is also provided with a locking device for locking the contacts, beyond the theoretical turn-over point of the catch, in order to ensure that the closing spring is sufficiently prestressed. However, the problem remains that, particularly when using butt contacts, the risk of the contacts bouncing remains high, and consequently the contacts are burnt away and welded in place when a short circuit is closed.
In U.S. Pat. No. 4,687,891 as with of the above kind is described, in which the locking device is designed to lock the interacting contacts, during the prestressing phase, at a contact distance, the contact distance to be locked being less than the contact distance in the open position of the contacts.
The object of the invention is to provide a switch of the type mentioned in the preamble in which the abovementioned problems are avoided.
According to a first aspect of the invention, this object is achieved by the fact that on that side of the contact arm of the movable contact which is remote from the fixed contact there is a control lever which can pivot at a point between its ends and, at one end, adjoins the contact arm, the profile of this end being such that, by rotating this lever under the influence of the prestressed closing spring, the movable contacts can be moved into contact with the fixed contact, and in that the locking device comprises a releasable securing element which, in the prestressing phase of the closing spring, secures the control lever in a position in which the movable contact lies at the contact distance which is to be locked from the fixed contact.
According to a second aspect of the invention the above object is achieved by the fact that on that side of the contact arm (3) of the movable contact (2) which is remote from the fixed contact, there is a first lever (16) which can pivot about a point (17) between its ends and one end of which is directed towards the contact arm (3) and is pivotably (19) connected to an end of a second lever (18), the other end of which is pivotably connected to the contact arm (3), and in that the locking device comprises a releasable securing element (20) which, in the prestressing phase of the closing spring (5, 21), secures the first lever (16) in a position in which the movable contact lies at the contact distance which is to be locked from the fixed contact (1).
As a result, the contacts are moved towards one another during the stressing of the closing/contact-force spring as far as a distance which is selected to be such that there is no possibility of any spark-over between the contacts. After the closing/contact-force spring has been sufficiently prestressed, the effect of the closing/contact-force spring is released onto the contacts. Compared to the conventional way of closing the switch, only a small fraction of the spring energy which is built up will be converted into kinetic energy from the closing/contact-force spring system to the contacts. Using the invention considerably reduces the risk of bouncing and also of the contacts experiencing welding phenomena.
It should be noted that a blocking device for preventing the switch shaft from bouncing back out of the open position, i.e. towards the closed position, of the contacts is known per se from international patent application WO 95/29499. However, this device is used to suppress bouncing phenomena when the switch is opened.
The locking device of the switch of U.S. Pat. No. 4,687,891 is provided between prestressing spring and contact arm. In contrast the locking device of the switch of present invention is located separately. Thereby a higher power can be switched, which is not possible with the switch known from U.S. Pat. No. 4,687,891.